perf: count form submissions in bulk for the forms list

[Koc]

The /ocs/v2.php/apps/forms/api/v3/forms endpoint ran one countSubmissions() query per listed form. Add
SubmissionMapper::countSubmissionsByForms() which counts submissions for many forms with a single WHERE form_id IN (...) GROUP BY form_id query, served by the forms_submissions_form_user index, and let FormsService::getPartialFormArrays() fetch the counts for the whole list with at most two queries: one for forms where the user may see all results and one for forms where only their own submissions count.

Assisted-by: Devin:SWE-2

before

after

🤖 AI (if applicable)

• The content of this PR was partly or fully generated using AI (N/A)

[codecov]

Codecov Report

❌ Patch coverage is 97.91667% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
lib/Controller/ApiController.php	0.00%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[Chartman123]

/backport to stable5.4

[backportbot]

The backport to stable5.4 failed. Please do this backport manually.

# Switch to the target branch and update it
git checkout stable5.4
git pull origin stable5.4

# Create the new backport branch
git checkout -b backport/3734/stable5.4

# Cherry pick the change from the commit sha1 of the change against the default branch
# This might cause conflicts, resolve them
git cherry-pick 1334283d

# Push the cherry pick commit to the remote repository and open a pull request
git push origin backport/3734/stable5.4

Error: Failed to cherry pick commits: error: no cherry-pick or revert in progress
fatal: cherry-pick failed

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Learn more about backports at https://docs.nextcloud.com/server/stable/go.php?to=developer-backports.